Throughout the filming of THE EXORCIST, with all the visual challenges entailed, one issue had never been resolved  how to make Regan MacNeils voice sound as powerfully horrendous as Blattys screenplay demanded. Even before shooting began, sound recordist Chris Newman and audio expert Ken Nordine had attempted to find a way to distort Blairs own naturally childish tones and twist them into something demonic and overpowering. The results were poor, producing merely an electronic growl with none of the threatening subtleties implied in both the novel and script.

As Friedkin now candidly admits; "When I started making THE EXORCIST, I had no idea how we were going to do the demon voice. Bill Blatty gives you a clue in the novel, saying that its something horrific, horrendous, shattering, booming, whatever...but how do you actually achieve what those adjectives suggest? When we were filming those scenes, Linda Blair did all the original dialogue, which Chris Newman recorded. Then we went back and forth with Ken Nordine doing some experimentation, both with Lindas voice, and with his own voice, fed through a computer, distorted and amplified. When I listened to the result I was extremely disappointed because it just sounded like a mans voice dubbed onto the face of a child. I just couldnt figure out how to fix it, because I knew I wanted a voice that was neutral, neither male nor female, but with both male and female characteristics. Who the hell sounds like that? Who has ever sounded like that? In the end I just threw myself on the mercy of the movie god and the name Mercedes McCambridge came into my head.

"McCambridge was a great actress who had won an Academy Award™ for her work in ALL THE KINGS MEN but before that she had done a number of memorable radio programs for people like Orson Welles. It turned out she was in Dallas, Texas, doing WHOS AFRAID OF VIRGINIA WOOLF on stage. I spoke to her on the phone, and to my joy she sounded exactly as she had sounded thirty years earlier on the radio. I told her about this project that I was working on, and she agreed to come and see it."

"We flew her out to Los Angeles and she watched the picture and said; OK, Ill have a crack at it. In fact I think I can do most of it with my own voice. So then we went into a sound-stage at Warner Bros. where she worked for maybe three weeks doing the demon voice. And she really went for it. She was chain-smoking; swallowing raw eggs; getting me to tie her to a chair; all these painful things just to produce the sound of that demon in torment. And as she did it the most curious things would happen in her throat. Double and triple sounds would emerge at once, wheezing sounds, very much akin to what you can imagine a person inhabited by various demons would sound like."

"It was really something else. Shed just sit there in that chair looking at the screen and go Aaaaaaaarghh and you would hear these things multiplied in her throat; these strange counterpoint noises; little skittering whistles and strange creaking rattles. When she was done, we took the speech that she had dubbed to Linda Blairs mouth, and occasionally we enhanced it, adding animal noises and sounds. But basically she performed it, under great duress. She knew exactly what was needed to go out and produce this effect, and I was stunned at what she put herself through, and what she allowed me to put her through in order to accomplish this. It was way beyond the call of duty, and if you were going to say that there was a single element that really made the film, then it could well be the sound quality that she achieved. It was pure inspiration."

The involvement of Mercedes McCambridge on the soundtrack of THE EXORCIST later became a source of heated controversy when Warners failed to credit her on the first run prints of the movie. Exactly why McCambridges name was initially omitted from the credits is unclear: Friedkin claims she specifically declined any on-screen acknowledgement, while McCambridge insists she fully expected it. Whatever the truth, her name appears on all but the first thirty-odd prints of THE EXORCIST, although not specifically as "The Voice of the Demon" as she would have preferred; instead her credit reads simply "And Mercedes McCambridge".

Along with McCambridges extraordinary vocal performance, the rest of the soundtrack of THE EXORCIST was gradually shaping up as even more experimental and avant garde than the movies elaborate visuals. While Ron Nagle recorded and altered the sounds of angry bees and slaughtered pigs to be blended into the final track, Friedkin tracked down a little known sound artist whose work he had stumbled upon in Alexandro Jodorowskys acclaimed cult movie EL TOPO to further enhance the sounds of the exorcism.

"That film had the greatest soundtrack I had ever heard," Friedkin enthuses. "I saw it at a midnight screening while I was preparing THE EXORCIST and I said to associate producer David Salven, Find out who did that sound, its just unbelievable. He did some research on this film which was made in Mexico, and came up with a guy named Gonzalo Gavira. He was sort of a barefoot Mexican peasant who used only natural objects to achieve sound effects.

"Eventually, we located Mr. Gavira, who spoke not a word of English, and we brought him here with his cousin who lived in L.A. and who translated for him. We showed him the film and although he didnt understand any of the words he got what was going on, and he indicated that he was happy to do the sound effects. So I said, Well what does he need? and the guy who was with him said, He doesnt need anything, just give him a microphone and hell do everything."

"So we opened up a mike, and Gonzalo Gavira actually stood there watching the film, and using his body and any objects that he could find around him  like cans or pieces of paper  to create a lot of the sounds you hear in the film. At one point he borrowed an old cracked leather wallet which contained some credit cards, and he held it up to the microphone and twisted it. And that sound was used in the movie to create the sound of the little girls head turning around. So that, and a number of other impressionistic sounds were created by a Mexican peasant who had no shoes."

Along with Gaviras unique contributions to the soundtrack of THE EXORCIST, other elements were included from anybody who had a good idea to contribute. According to film editor Bud Smith, "we had one guy who brought a band saw into the recording studio. It was all tied up, then they cut it loose and threw it into the air, and it made this wonderful whoosh kind of a sound. Then we also took the sound of a wind-harp thats up there in the rocky mountains in Colorado  the wind blows through it and it makes this kind of eerie noise. And all these sounds were incorporated onto the soundtrack somewhere."

The man responsible for bringing all these elements together was dubbing mixer Buzz Knudson, who had worked with Smith on ELECTRAGLIDE IN BLUE, and whom Friedkin credits with creating the "soundscape" of THE EXORCIST.

"The sound effects are probably the biggest part of the movie," Knudson acknowledges, "and Billy was a real perfectionist about it. All the sound effects were hand picked by him because he really had his thumb on the picture. Hes so meticulous, and because of that I think it ended up taking us fifteen weeks to do that track, which is an eternity today. Today you mix a movie in five to six weeks. But it was worth it, because it turned out great."

For Friedkin, the key to the power of the soundtrack lay in the way it mirrored and counterpointed the extreme visual shifts which he had marshalled on screen. "I had deliberately conceived the film with scenes that contrasted light and dark," Friedkin elaborates, "so you would get these blazingly bright scenes, as in Iraq or in the cold light of Georgetown in the Fall; and then there would be these dark scenes in the attic and the exorcism room and so on. Onscreen, the whole film alternated between the forces of light and dark, and when it came to the soundtrack, I wanted the same kind of contrast."

"I had grown up listening to the classic radio dramas of the forties and fifties, and in many ways they really provided the inspiration for the soundtrack of THE EXORCIST. I always consider the soundtrack as something quite separate from the film, very often not in synch with the film but in contrast to whats on the screen. In this case I felt that the soundtrack should have a dynamic that swung between very loud, piercing oppressive noises, and absolute, total dead silence. And many times in order to achieve that silence I actually had the sound-guys use white leader tape rather than blank magnetic tape so that when the track went quiet, there was nothing on it whatsoever."

In generating the shifts between loud noises and chasmic silences, Buzz Knudson understood that Friedkin was again reaching for the extreme. "Billy has an extremely keen ear," says Knudson, "and in the quiet scenes, if there was any hiss at all, or any noises, he would hear them. He could pick up sounds that only dogs could hear! So wed have to work on it and work on it, until we got it all clean enough for him. Personally, Id never heard those levels of sound contrast before, going from like the loud sounds of the X-Ray going up and down and the bang! to nothing. Absolute silence! It was just a great idea. In the same way that Billy would tell the cameramen just the right flavour of color he wanted on screen, from bright to dark and so on, he would do the same with the soundtrack."

Friedkins extreme attention to the detail of the soundtrack pervaded every scene from the Iraqi prologue, to the street scenes of Georgetown, to the hellish netherworld of the exorcism itself. "Youd think that finale would have been the most complicated segment," states Knudson, "and those scenes were tough because theres such a mix of sounds in there. Youre hearing the two priests talking; youre hearing the bed shaking; youre hearing the demon breathing or Mercedes McCambridge wheezing; youre hearing all those things at the same time. Theyre all important and I think we ended up playing them all at almost the same level. It worked great because you can still hear enough of the exorcism dialogue against the counterpoint of the thumping of the bed and all the rest of it.

"The exorcism scenes were complicated, but the thing is the whole film was like that. The Iraq opening, for example  that dig was a real challenge. It was just so involved with all the effects, the chipping, the picks, the hammers, the anvil, everything thats going on in each shot. Every time youd look at the people on the hill, if there wasnt a sound for what they were doing youd have to put one in. There were just so many people in each shot, and your eye always seems to go to the one youve missed. Billy would never miss anything, though, and hed always be right there telling us what changes to make. In the end we figured that the only way to get a reel finished was to send him away and let us do what we thought was right, then have him come back later in the day and listen to it, and make changes  and he made a lot of changes."

"Theres one part of the film which really showed me the kind of person Billy is," Knudson remembers fondly. "Its near the beginning, when Ellen Burstyn comes down the steps of Georgetown University, and she tells her driver that shes going to walk home. As she walks around the corner, a lady passes her, and the ladys got a bag in her hand. Billy worked a whole day on that bag. He didnt like the sound of the first bag, so we got another bag and it had to hit her leg just right and it had to be just the right level. So now, every time I see that scene, I think how much time we spent on it, and what a perfectionist Billy was to get what he wanted."

"But the really surprising thing about THE EXORCIST," concludes Knudson, "is just how different its soundtrack is to the tracks you hear today. Just before we started remixing the picture for this new anniversary edition, we ran an old print of the film and we were amazed by how much the style of mixing has changed. What we did back then was very instinctive; you put the dialogue in the way it feels right, you play the effects and the backgrounds for whatever emotions you want to get out of them. But today the dialogue is all in your face, the sound effects are in your face, the musics right up there and they just beat you over the head with them all for hours. Thats completely different to THE EXORCIST which was actually often a very silent movie  a loud silence."

It was this sense of "loud silence" that Friedkin wanted to preserve throughout the soundtrack, including the musical score. Having failed to make a harmonious connection with PSYCHO scorer Bernard Herrmann, (who had suggested composing the music for THE EXORCIST, to be performed on a large church organ in London) Friedkin had turned to Argentinian-born composer Lalo Schifrin. According to Friedkin, he directed Schifrins attention toward the often atonal work of such contemporary composers as Krzysztof Penderecki and George Crumb, suggesting that he take a cue from their efforts. Somehow, his suggestions struck the wrong chord with Schifrin.

As Buzz Knudson remembers it, "We were just starting work doing some predubbing on the picture, and Billy got a phone call from Lalo. He said, Come on Buzz, were going to go over and listen to the main title, theyve just finished doing it. So we went over to hear what was going on. And over on the scoring stage there was, I believe, a ninety piece orchestra. So Billy said ,OK, Lalo, lets hear it. Anyhow, Lalo was sitting there and they played this score, which was a beautiful score, but a big full score that would have dominated the movie. When it was over, there was a kind of silence. And Billy got out of his chair and said, Well, Lalo, its never going to be in my movie. And that was it."

The following day, Friedkin contacted Jack Nitzsche and asked him to provide some atonal linking pieces which would sit alongside segments of recordings by Penderecki, Crumb, Hans Werner Henze and Anton Webern which he now intended to use in THE EXORCIST. Nitzsche went to work, experimenting with vibrating crystal stemware to provide the gently hypnotic howl which now opens the film, and which also accompanies Father Merrins legendary arrival at the house on Prospect Street. Elsewhere, Friedkin used a few phrases from the opening of Mike Oldfields "Tubular Bells" which he perceived as an innocent nursery-rhyme-style theme for Regan. It has since become recognised as the "Theme from THE EXORCIST".

Meanwhile, Bud Smith kept wondering what to do with the tape of Schifrins unused music. "After all, it was there," he states. "I think one day we were on the dubbing stage over at Todd AO and we tried to slip some of it into the party scene, where theres just this background of muzak playing. We played in a bit of Lalos score and Billy said, Give me that tape. So we took the music off the recorder, handed it to him, and he went out the front of Todd AO and threw the tape across the parking lot.

"After that we reverted back to classical music, which Billy really likes to listen to anyway. I think his ideal life would be to sit and read and listen to classical music. So he just kept bringing in stuff, much of which wasnt even really "music"  they were more like atonal orchestrations, strange pizzicato sounds. If you listen to the film, a lot of the time you dont know whether what youre listening to is music or sound effects.

"I wanted the overall effect to be like a cold hand on the back of the neck," Friedkin now says of the soundtrack of THE EXORCIST. "My feeling is that thanks to the work of people like Buzz Knudson and Jack Nitzsche thats exactly what we got. A lot of it is almost imperceptible, with the "music" blending into the sounds of the landscape. Never controlling a scene. I never planned to put music in any of the "big moments", because the so-called big scenes carry themselves in my view."

Its a sentiment shared by Max von Sydow: "It would have been so easy for Billy to use a lot of threatening build-up music," he reflects, "to use that to make us understand through the music that now something terrible is going to happen. It would have been a big mistake. It works so much better the way it is now."